This invention relates to an active matrix drive fluorescent display device and a method for manufacturing the same, and more particularly, to an active matrix drive type fluorescent display device in which a semiconductor chip having a plurality of anodes individually driven and arranged in a matrix-like manner thereon is fixed on an inner surface of a substrate of an envelope and which is constructed so as to prevent misluminescence of the anodes due to a failure in insulation between, electrodes.
A conventional active matrix drive fluorescent display device typically includes an envelope constructed of a substrate made of an insulating material such as glass or the like and a casing sealedly mounted on an upper surface of the substrate. The substrate is mounted thereon with a silicon wafer of a rectangular shape acting as a semiconductor chip while being positioned in the envelope. The semiconductor chip has luminous sections arranged in a matrix-like manner thereon. The rectangular silicon wafer is made by slicing a purified or high-purity silicon monocrystal of a circular cylindrical shape into a disc-like shape. The disc-like silicon wafer thus formed is provided thereon with a plurality of rectangular elements each having a required structure incorporated therein. Then, the rectangular elements are cut off.
Such a conventional active matrix drive fluorescent display device will be further described with reference to FIG. 4.
A silicon wafer 100 of a rectangular shape is adhered to a substrate 101 by means of a die bonding paste 102. The silicon wafer 100 is provided on an upper surface thereof with anodes 105 in a matrix-like manner, each of which includes an anode conductor 103 and a phosphor layer 104 deposited on the anode conductor 103. The anodes 105 each are provided thereunder with a transistor acting as a switching element. The silicon wafer 100 is provided on the upper surface thereof with a flat control electrode 106 of a lattice-like shape so as to extend between the anodes 105 adjacent to each other. The active matrix drive fluorescent display device also includes filamentary cathodes 107 stretchedly arranged above the silicon wafer 100 so as to act as an electron source while being positioned in an envelope. The cathodes 107 each include a core wire 107a made of a material generating heat due to feeding of a current thereto such as tungsten or the like and an electron emitting substance 107b deposited around the core wire 107a. The electron emitting substances include oxides of alkaline earth metals including Ba and the like.
The active matrix drive fluorescent display device thus constructed is driven in such a manner that any desired one(s) of the anodes 105 arranged on the silicon wafer 100 is selected by means of the switching element and electrons emitted from the filamentary cathodes 107 are impinged on the phosphor layer 104 of the anode 105 selected. The control electrode 106 has a positive potential constantly applied thereto, so that electrons emitted from the cathodes 107 may be diffused or spread by the control electrode 106, resulting in being uniformly fed to the anodes 105. Such selective driving of the desired anodes 2 in arranged in a matrix-like manner for luminescence leads to any desired graphic display.
During actual driving of the active matrix drive fluorescent display device, the electron emitting substance 107b of each of the cathodes 107 is activated to produce free metal, which tends to adhere to the silicon wafer 100. For example, in the conventional fluorescent display device described above, the electron emitting substance 107b produces free barium (Ba), which tends to adhere to a cut surface 110 of the silicon wafer 100 which is an outer peripheral end surface of the silicon wafer 100 formed by cutting off it from the disc-like silicon monocrystal, as well as to a periphery thereof.
The outer peripheral end surface of the silicon wafer 100 shown in FIG. 4 constitutes the cut surface 110 of the silicon wafer formed by cutting off it from the disc-like silicon wafer. The cut surface 110 of the silicon wafer 100 is constructed into a laminate structure having the above-described die bonding paste 102, a p-type layer 100a, an n-type layer 100b and an insulating film 100c upwardly laminated on each other in turn. The p-type layer 100a is adhered to the substrate 101 through the die bonding paste 102, resulting in providing a portion rendered electrically GND or an electrically GND portion. Such adhesion of free Ba to the cut surface 110 as described above keeps the insulating film 100c from carrying out is function, resulting in the electrically GDN portion of the cut surface 110 leading to a failure in insulation between the anodes 105 (phosphor layers 104) and the control electrode 106.
Such a failure in insulation causes the anodes 105 to be actually unintendedly turned on when the control electrode 106 is kept turned on, even when the anodes 105 are kept turned off, resulting in electrons impinging on the phosphor layers 104 of the anodes 105, leading to misluminescence of the phosphor layers. Such misluminescence tends to occur at the phosphor layers 104 positioned in proximity to the cut surface 110 of the silicon wafer 100.
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present invention to provide an active matrix drive fluorescent display device which is capable of preventing misluminescence of phosphor layers due to a failure in insulation between electrodes owing to adhesion of a conductive material to a cut surface of a silicon wafer arranged in an envelope and formed thereon with luminous sections in a matrix-like manner.
It is another object of the present invention to provide a method for manufacturing an active matrix drive fluorescent display device which is capable of providing an active matrix drive fluorescent display device attaining the above-described object.
In accordance with one aspect of the present invention, an active matrix drive fluorescent display device is provided. The active matrix drive fluorescent display device includes an envelope, a semiconductor chip arranged on an inner surface of the envelope, and a plurality of anodes arranged in a matrix-like manner on the semiconductor chip and individually driven. The anodes each have a phosphor layer deposited thereon. Also, the fluorescent display device includes filamentary cathodes arranged in the envelope so as to be positioned above the semiconductor chip. The semiconductor chip is covered on an end surface thereof with an insulating material.
Also, in accordance with this aspect of the present invention an active matrix drive fluorescent display device is provided. The active matrix drive fluorescent display device includes an envelope including a substrate, a semiconductor chip arranged on an inner surface of the substrate of the envelope, switching elements arranged in a matrix-like manner on the semiconductor chip and selectively driven, anodes each arranged on each of the switching elements and having a phosphor layer deposited thereon, a control electrode arranged on the semiconductor element in a manner to extend between the anodes adjacent to each other, and filamentary cathodes each including an electron emitting layer made of a metal oxide and arranged in the envelope so as to be positioned above the semiconductor chip. The semiconductor chip being covered on a cut surface thereof with an insulating material.
In a preferred embodiment of the present invention, the insulating material is a fine powder of a material selected from the group consisting of Al2O3, SiO2, ZrO2 and frit glass.
In a preferred embodiment of the present invention, the semiconductor chip is formed at a part of a portion thereof in proximity to an outer edge of an upper surface thereof with an electronic element other than the anodes and switching elements. The insulating material is arranged on a cut surface of the semiconductor chip other than a cut surface thereof in proximity to the electronic element.
In accordance with another aspect of the present invention, there is provided a method for manufacturing an active matrix drive fluorescent display device including an envelope including a substrate, a semiconductor chip arranged on an inner surface of the substrate of the envelope, anodes arranged in a matrix-like manner on an upper surface of the semiconductor chip, selectively driven and each having a phosphor layer deposited thereon, and filamentary cathodes arranged in the envelope so as to be positioned above the semiconductor chip. The method includes the step of coating a liquid on a cut surface of the semiconductor chip fixed on the substrate of the envelope. The liquid is prepared by dispersing a fine powder of an insulating material in a solvent. The method also includes the step of calcining the substrate to cover the cut surface of the semiconductor chip with the insulating material.